The present invention generally relates to a liquid separating apparatus using a permeation evaporating method.
Generally, in the field of a chemical industry, so-called organic solvents such as alcohol and its kind, kent and its kind, either and its kind, ester and its kind, and so on are often used. All these organic solvents are likely to dissolve water, and are very dissolved in water in quality. Accordingly, they are likely to become generally mixed water even in the preserving condition so as to form an azeotropic mixture with respect to the water.
However, when the organic solvent is used in actual chemical reaction, the extremely high purity is demanded, with a strict limit being imposed upon the mixture of the water. Thus, in the actual use, a concentration system is generally adopted of increasing the purity through the separation of the water from the organic solvent as the prior treatment step.
Also, in a step of washing precision components such as semiconductors or the like, the product is washed with pure water, thereafter with, for example, isopropanol (namely, alcohol group washing liquid) so as to completely remove the moisture adhered in the former step. At this time, the isopropanol as the washing liquid is diluted by the repeated use thereof through the moisture of the former step. When the washing operation is effected by the use of the isopropanol diluted into the concentration of 90% or lower, the moisture remains on the product, which may cause defects in the portion thereof. Therefore, there is required a regenerating system which separates the water from the isopropanol diluted by the use in the precision washing operation so as to increase the purity for the reuse thereof.
Conventionally a distillation method was generally used as a method of separating the water (pure water) from the mixed liquid between such water as described hereinabove and organic solvent such as alcohol or the like so as to concentrate the organic solvent.
However, in the case of the distillation method, it is difficult to separate azeotropic mixture, approximate boiling point mixture of the like in terms of the principle thereof. As the mixture between the above-described water and alcohol (ethanol, isopropanol or the like) corresponds to the azeotropic mixture, the separating operation cannot be effected by the conventional general distillation method.
In such a case as described hereinabove, although a so-called azeotropic distillation method which makes it possible to effect an separating operation through the addition of the given tertiary component such as benzene, trichloroethylene or the like may be adopted, the method consumes an extreme large quantity of steam consumed in this method, with many problems that the separation liquid is polluted by the tertiary component mixture, the apparatus is complicated, and so on.
Among the especially active researches, developments in recent years with such circumstances being backgrounds, there is a separation (dehydration) system for water/organic liquid mixture by a liquid separation method using, for example, moisture selective transmission membranes (for example, as disclosed in Japanese Patent Application No. 62-35401).
In the liquid mixture separating system, a primary chamber and a secondary chamber are partitioned, in the primary chamber a separating operation is effected by a moisture selective transmission membrane composed of a non-porous amorphous high molecular membrane, with the object mixed liquids containing the water being fed into the primary chamber, in the secondary chamber the transmitted separation component of an object is condensed and stored. The secondary chamber side is pressure-reduced into a vacuum condition by a pressure reducing means such as a vacuum pump or the like so as to form a partial pressure difference of the given value or more between the primary chamber side boundary face of the water selective transmission membrane and the secondary chamber side boundary face. The water molecule (H.sub.2 O) only transmitted through each step of adsorption.fwdarw.resolution.fwdarw.diffusion.fwdarw.disconnection is adapted to go out in a gaseous condition onto the side of the secondary chamber on the low pressure from the high pressure (the primary chamber side) in accordance with the partial pressure difference and the concentration difference of the selection component between the primary side of the secondary side.
Accordingly, according to the mixed liquid separating system of such a construction as described hereinabove, not only the approximate boiling point mixed liquids, but also such azeotropic mixed liquids such as the above-described water and alcohol may be separated, concentrated without any questions. Furthermore, as the tertiary component as in the azeotropic distillation method is not used at all, with an advantage that the operation is clean, and the apparatus is also compact.
In the actual system, the construction through the combination between the primary chamber and the secondary chamber as described hereinabove uses modules as a single unit, and a plurality of pair combinations with them are often used as plant.
As the permeation evaporating operation in the liquid separating apparatus is a separating operation substantially accompanying a phase variation (liquid phase.fwdarw.gas phase) as clear from the above-described explanation, the temperature of the feed liquid around the permeation membrane is gradually lowered due to the evaporation latent heat of the transmission material as the separating condition is advanced. And the transmission speed in the transmission membrane portion has an exponential function relation with respect to the temperature of the feed liquid, and is higher as the molecular activity becomes active with the temperature being higher. Accordingly, when the temperature of the feed liquid is lowered as described hereinabove, the transmission speed of the object liquid is lowered to deteriorate the separation efficiency, which has been an important technical solution task.
In a certain quarter, for example, an independent heat exchanger for heating use is established on the way to the external passage of the module with respect to such technical task, and the mixed liquid lowered in the temperature is fed into the separation module of the next stage, while the mixed liquid is being heated. In such a method, considerable temperature difference of the mixed liquids is caused between on the entrance side within the separation module and the output side thereof, thus failing in the sufficient solution of the problem.
On the other hand, as the liquid separating system by the liquid separating method using the selective transmission membrane is adapted to efficiently transmit only the selection component which becomes an object in the selective transmission membrane portion, a so-called concentration boundary membrane (concentration boundary layer) is formed, because the selection molecules which become separation objects become short in the mixed liquids near the selective molecule adsorption face of the transmission membrane as the flow of the mixed liquids on the primary chamber side is slow, so that the necessary concentration difference may not be retained, with a problem that the transmission speed, and transmission efficiency are deteriorated even by it or as in the case of the above-described temperature.
In the liquid separating method using the selective transmission membrane, the concentrating operation of the mixed liquids may be effected. But it is difficult to remove the dirt of the isopropanol in a case where the diluted isopropanol used as, for example, precision washing liquid is concentrated and is used again, with a problem that it is improper in the reuse of the washing liquid.